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Does brain activity mean Ariel Sharon will wake up from coma?

Medical professionals from Ben-Gurion University are reporting that former Israeli prime minister Ariel Sharon showed significant brain activity when undergoing testing.

CNN reported that scientists scanned Sharon's brain using a functional MRI (fMRI), a scan that measures blood flow in the brain, at Soroka University Medical Center in Beersheba, Israel last week. They first showed him pictures of random houses and his own home. More blood flow was observed in the brain when Sharon saw his house. A similar effect was shown when Sharon was played audio of his son speaking gibberish versus coherent language. The progress was called "encouraging" yet "subtle."

"We know that he can process pictures -- pictures of faces," Dr. Alon Friedman of Ben Gurion University told CNN. "And he can even differentiate between pictures of faces and pictures of houses, pictures of his family to other objects. He can differentiate between words that were spoken to him by his son, compared to a noise."

But, expert neurologists cautioned to CBSNews.com that just because there was brain activity doesn't mean that the Israeli leader would be waking up from his coma any time soon. Sharon has been in a vegetative state since Jan.4, 2006 when he suffered a stroke and brain hemorrhage.

"Functional MRIs measure brain cortical activity -- presumably where we think, hear or perceive -- but it doesn't mean that he is conscious in any way that we understand it," Dr. Michael Schulder, the vice chair of the department of neurosurgery at North Shore University Hospital in Manhasset, N.Y., told CBSNews.

Schulder, who was not involved in Sharon's case, said fMRI's measure activity in the cortex, which is the area of the brain that directs movement and speech and can perceive speech, touch and vision. While it can be a useful tool for surgeons and can diagnose early Parkinson's disease or Alzheimer's, it cannot show widespread brain activity.

Dr. Benjamin Emanuel, an assistant professor of neurology and the fellowship director for the Division of Neurocritical Care at Keck Medical Center at the Unversity of Southern California in Los Angeles, said similar tests to Sharon were done on other patients in 2006. Both vegetative patients and non-vegetative patients were asked to complete a task -- for example, imagine that they were playing tennis -- while their brains were being scanned. Though both groups' brains showed similar activity despite what state they were in, scientists still doesn't know what this means exactly.

"It means perhaps that these patients weren't vegetative or perhaps there is some processing going on that we're unaware of. What does it mean for his (Sharon's) future? No one really knows," Emanuel, who was not involved in Sharon's study, said.

Both doctors cautioned that typically signs of improvement need to be observed within a few months from the injury for there to be a chance of recovery. Emanuel said for stroke patients, signs of progress need to be observed within six to 12 months from the incident, and the older you are the less likely you are to recover.

Instead of just relying on scans, doctors usually look for physical signs that are only observed using "good-old fashioned (TV show character) Dr. Marcus Welby bedside manner," Schulder said. Schulder said he usually looks for positive movement in a patient such as tracking an object with their eyes within the first month after the injury. Then progressive steps, such as movement in the limbs or following commands to lift a thumb should be observed in the following months.

"You basically want improvement," Emanuel said. "Over time, the longer you go without improvement the less likely you are going to improve."

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